The invention relates to arrangement of the propulsion nozzles for gas turbine engines in particular to by-pass gas turbine engines.
Control of the mixing and distribution of the exhaust jet plumes can be used to reduce the noise from gas turbine engines. Several methods have been tried to effect this and have resulted in differing degrees of effectiveness. Most methods result in significant thrust losses or increased weight.
U.S. Pat. No. 4.288,984 discloses a number of ways in which the mixing and distribution of the exhaust jet plumes is controlled in a by-pass engine. These include having a swept, canted or off-set primary nozzle.
It is an object of the invention to provide an improved nozzle design for by-pass engines which offers a significant reduction in noise while maintaining high efficiency.
The invention comprises a by-pass gas turbine engine including a primary and a secondary nozzle wherein the primary nozzle is situated radially within, but axially protruding from, the secondary nozzle characterised in that the primary and secondary nozzles have a substantially common central axis along their lengths and that the direction of airflow exiting at least one of the primary or secondary nozzles is at an angle to the central axis of the engine and the direction of airflow exiting each nozzle is at an angle to the other thereby promoting preferential distribution and mixing of the airflows.
This promotes mixing and dilution of the airflow and shielding the higher velocity jet by a greater proportion of the bypass flow, causing the noise to be convected to angles closer to the engine axis.
In one embodiment of the invention both the primary and secondary nozzles are truncated at oblique angles. The nozzles are preferably orientated such that said oblique angles are opposite directions. The exit plane of the airflow is therefore not perpendicular to the central axis defined by the nozzle.
In an alternative embodiment the flow direction of the primary nozzle axis is simply orientated at a small angle to the axis of the secondary nozzle.
In a further embodiment of the invention the internal profile of one or both nozzles is asymmetric such that the primary flow exits the nozzle at an angle to the secondary flow.